1. Field of the Invention
This invention relates to the use of certain enzyme compositions which may be incorporated in a dough or sponge to improve softness and retard staling of baked goods.
2. Description of the Related Art
The phenomenon of bread staling is not completely understood. The staling of bread is usually related to the retrogradation of starch, or the association of starch molecules to form areas of crystallinity which result in an increase in firmness of the bread with the passage of time. Staling is of considerable economic importance to wholesale bakeries since it limits the shelf life of baked goods in retail outlets to about 3 or 4 days, plus several additional days in the home of the consumer after purchase. The short shelf life of the baked goods has required wholesale bakeries to have separate distribution systems that operate independently of the usual channels for packaged food distribution. In addition, the market area of a bakery is generally limited by the maximum radius the distribution system can cover within 24 hours.
Cereal chemists and bakery technologists have found that various chemical emulsifiers have some influence in extending the shelf life of baked goods, such as bread. However, chemical emulsifiers are only partially effective in reducing bread staling. Monoglycerides and other emulsifiers have been added to bread to improve its softness. Although these emulsifiers produce a softer bread, they have little influence in reducing the rate of bread staling. The term "baked goods" also connotes application to such products as rolls, muffins, biscuits, donuts, crackers and cake.
Enzymes of various types have been used in baked goods and some have been used for the specific purpose of inhibiting staling.
Cereal alpha-amylase enzyme in the form of malted barley is commonly added to wheat flour for bread to standardize its baking performance. Cereal alpha-amylase is most active at a pH of about 6 and a temperature of about 70.degree. to 75.degree. C.
"Fungal alpha-amylase" enzyme as the term is used in the baking and enzyme industries, generally relates to enzymes made from Aspergillus oryzae, and can also be used to standardize baking performance. The enzyme is most active at a pH of about 6 and a temperature of about 50.degree. to 55.degree. C.
"Bacterial alpha-amylase" enzyme as the term is used in the baking and enzyme industries, most often refers to enzymes made from Bacillus subtilis, which are used to inhibit staling. The enzyme is most active at a pH of about 7 and a temperature of about 75.degree. to 80.degree. C.
U.S. patent application Ser. No. 07/419,980, filed Oct. 11, 1989, describes an acid stable microbial alpha-amylase enzyme which can be derived from a fungi but is distinct from the cereal, fungal and bacterial alpha-amylases referred to above. It has an optimum activity at a pH of about 3.0 to 5.0 and a temperature of about 60.degree. to 75.degree. C. This is one of the enzymes used in the enzyme composition of the present invention.
One enzymatic approach to retarding bread staling is disclosed in U.S. Pat. No. 2,615,810 to Stone and involves the use of a heat-stable bacterial alpha-amylase enzyme to attack gelatinized starch granules during baking.
A refinement to Stone's approach is described in U.S. Pat. No. 4,299,848 to DeStefanis et al. which discloses a process for the inactivation of the proteolytic enzymes present in commercially available heat stable bacterial alpha-amylase enzyme preparations obtained from extracts of Bacillus subtilis, Bacillus sterothermophilis or other microbial sources.
A further refinement is given in U.S. Pat. No. 4,654,216 to Carroll et al. which discloses the use of heat stable bacterial amylase in conjunction with pullulanase to overcome the problems of the Stone and DeStefanis et al. approaches. Carroll et al. further discloses that the baking art generally classifies alpha-amylases according to their source, as bacterial, fungal and cereal, also noting that the fungal amylases exhibit relatively low thermal stability and deactivate rapidly above 65.degree. C. Thus, fungal amylases are not contemplated for practice of Carrol et al.'s invention which comprises the addition of an enzyme mixture of cereal or bacterial alpha-amylase and a pullulanase to dough in proportions of from 0.25 to 5 SKB (alpha-amylase units) and 5 to 75 PUN (debranching enzyme units) per 100 grams of flour.
A drawback of the Stone, DeStefanis et al. and Carroll et al. approaches is the tendency of thermally stable bacterial and cereal alpha-amylases to remain active too long during baking and to cause gumminess in the finished product. As a result, these approaches require a degree of control over dosages and enzyme ratios which may be impractical to apply commerically.
U.S. Pat. No. 4,320,151 to Cole discloses that the thermal stability of a fungal alpha-amylase is substantially increased by dispersing aqueous solutions of the enzyme in concentrated sugar solutions. The sugar protected fungal alpha-amylase enzyme servives incorporation in a dough and remains active until a temperature is achieved at which starch gelatinization occurs. Thus, the sugar protected fungal alpha-amylase solutions retain their starch hydrolyzing activity, even when heated to temperatures well above those at which the enzyme would normally be completely denatured. However, the processing and ingredient changes required make this approach unsuitable for a number of bakery applications.
Russian Patent 659,617 discloses the production of a microorganism strain from which acid-resisting alpha-amylase and glucoamylase enzymes are obtained. The strain, Aspergillus niger 147-A, is obtained by treating Aspergillus niger 475 with ultraviolet radiation. In one example in the patent, bread was baked using an enzyme preparation of acid-resisting alpha-amylase and glucoamylase from A. niger 147-A, and was found to result in a slower staling process. The alpha-amylase is the product of a mutant strain of A. niger, not one readily available in nature, and the acid-resisting alpha-amylase produced from A. niger 147-A irreversibly loses its activity at a pH of 3.0.
Canadian Patent No. 980,703 to Grampp et al. discloses a thermolabile bacterial alpha-amylase that would not be prone to the gumminess problem of conventional bacterial alpha-amylases. However, this enzyme is not sufficiently temperature stable to inhibit staling and is not acid stable.
Vidal, U.S. Pat. No. 4,160,848, discloses an anti-staling composition which contains a combination of a glycerol ester of a fatty acid and other substituted and non-substituted fatty acids which are preferably combined with an enzyme selected from alpha-amylase, amyloglucosidase and mold derived lipase. Aspergillus oryzae derived alpha-amylases are disclosed as an example. The reference discloses the addition of the composition to dough or sponge.
G. Bussiere et al. in "The Utilization of Alpha-Amylase and Glucoamylase in Industrial Baking Technology", Annales De Technologie Agricole, volume 23 (2) pages 175 to 189 (1974) discloses studies on the role of alpha-amylases of bacterial origin and glucoamylase in bread making technology. This reference teaches that only alpha-amylases of bacterial origin are effective to retard staling.